Poxvirus K3 Orthologs Differentially Modulate NF-kB Activity through Targeting the PKR-eIF2a Phosphorylation Pathway

Myxoma virus (MYXV) is a rabbit-specific poxvirus. It causes an innocuous localized cutaneous fibroma in brush rabbits, its nature host. In contrast, the same virus exhibits up to 99.8 % fatality rates in European rabbits, causing the lethal disease myxomatosis. MYXV was deliberately released as a biocontrol agent against European rabbits in Australia and European. The subsequent results of coevolution are both attenuation of MYXV and increased resistance in rabbits. This provided us with one of the best documented examples of host-pathogen evolution and the opportunity to investigate the molecular mechanism underlying virulence changes after encountering with new hosts. In response to virus infection, host protein kinase R (PKR) can sense double-stranded RNA, which is generated during virus replication. Activated PKR phosphorylates the translation initiation factor eIF2a, resulting in the globally inhibition of protein synthesis. PKR has also been reported to involve in the regulation of other signaling pathways, including eIF2a/ATF4 responses and NF-kB activities. Poxviruses encodes two inhibitors, E3 and K3, to inhibit PKR mediated eIF2a phosphorylation and repress the inhibition of protein synthesis, facilitating virus replication. The molecular mechanisms behind PKR associated NF-kB activation and regulation of PKR associated NF-kB transcriptional activities by K3 orthologs are still largely unknown. The main goal of this study is to elucidate molecular mechanisms for the crosstalk between PKR-eIF2a antiviral pathway and NF-kB dependent pro-inflammatory response during MYXV infection. We examined the antiviral function of PKRs from diverse mammalian species during MYXV infection. Activation of PKR induced ATF4 responses and NF-kB transcriptional activities. Of note, rabbit PKRs from nature host and new host of MYXV showed different sensitivity to M156 inhibition. Higher inhibition of PKR inhibition exerted by M156 or other K3 orthologs from different poxviruses resulted in low level of NF-kB activation. In conclusion, our research reveals the interaction between PKR and K3 orthologs affect the outcome of NF-kB dependent pro-inflammatory response, possibly contributing to viral replication and pathogenesis in vivo